The thermocoloration of a water-soluble spiropyran, T,3',3'-trimethylspiro[2Ff-l-benzopyran-2,2'-indoline]-6-sulfonic acid (1), which has been newly synthesized in this work, in the anionic AOT reversed micelles has been investigated in order to evaluate the effect of the reversed micelles in controlling the reaction rates or pathways by restricting the mobility of the substrates being situated in a specific reaction field. The probe 1 showed a negative photochromism in polar solvents such as water, MeOH, and EtOH as well as in the AOT reversed micelles. The thermocoloration rates of 1 were retarded by about 20 times in the 0.2 M AOT/O.6 M H20/hexane micelles compared with those in MeOH in which microscopic polarity was comparable to that in the interior core of the reversed micelles adopted. This was explicable in terms of the restriction in the internal rotation of the 2,3 bond of 1 during the thermocoloration accompanied by the cis-trans isomerization in a largely restricted field as provided by the reversed micelles. The extent of deceleration in the thermocoloration in the AOT reversed Hydroboration Kinetics. 4. Kinetics and Mechanism of the Reaction of 9-Borabicyclo[3.3.1]nonane with Representative Haloalkenes.

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The association of nitroxide spin probes with aggregates of peptide-surfactants was investigated in aqueous media. The spin-labeled fatty acid was completely incorporated into the peptide-surfactants with anisotropic immobilization, while the less hydrophobic nitroxide radical was distributed between the hydrophobic and electrostatic regions of the aggregates. The peptide-surfactants may form tighter aggregates than the ordinary micelles.

In order to clarify micro-environmental effects on the reactivity of mercapto groups in enzymes, cationic surfactants bearing a mercapto group, N-hexadecyl-Nα-(3-trimethylammoniopropionyl)-l-cysteinamide bromide (CM·Cys-1) and N-dodecyl-Nα-(6-trimethylammoniohexanoyl)-l-cysteinamide bromide (CM·Cys-2), were synthesized and their kinetic behavior investigated. The surfactants above their critical micelle concentrations markedly catalyzed the decomposition p-nitrophenyl hexanoate (PNPH) and acetate (PNPA), the concentrationrate profiles being found to be those for typical micelle-catalyzed reactions. The rate constants for the degradation of PNPH as catalyzed by CM·Cys-1 and -2 in the micellar phase are 0.482 and 0.197 s−1, respectively, in 9.8% (v/v)ethanol–1.0%(v/v)dioxane–1.0%(v/v)methanol-water at 30.0±0.1 °C, pH 8.65, and μ0.10 (KCl). The difference in catalytic activity can be attributed partly to the micro-environmental effect on the pKa value of the mercapto group lying at the reaction center. The rate constants for the thiolate anions (true reactive species) of CM·Cys-1 and -2 to react with PNPH were identical with each other irrespective of the nature of the surfactants. The electrostatic effect provided by the cationic charge in the Stern layer, which acts to reduce the pKa value of the reactive mercapto group, seems to play a more important role than the desolvation effect on the thiolate anion by the hydrophobic field.

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Decarboxylation reaction of 6-nitro-1,2-benzisoxazole-3-carboxylate (1) in cationic and anionic reversed micelles has been investigated with particular attention to the microenvironmental effect, such as microviscosity, micropolarity, and microactivity, in the specific and restricted reaction field as provided by reversed micelles. In 0.20 M CTAC/0.32 M H2O/CHCl3 reversed micelles, the reaction was accelerated about 1300-fold compared with that in bulk aqueous solution. Of various surfactant aggregate systems such as aqueous micelle, bilayer, and reversed micelle, the cationic reversed micelle could provide the most effective reaction field for the present decarboxylation reaction. This reaction is never accelerated in an anionic aqueous micelle. However, in the anionic AOT reversed micelle, the reaction was apparently accelerated by both lowering the micropolarity and increasing the microviscosity around the substrate. The unique rate enhancement for the decarboxylation reaction of 1 provided by reversed micelles was interpreted in terms of the “multiple field assistance.”

In order to obtain a clue to understanding the micro-environmental effect on the reactivity of a mercapto group placed in a reaction center of enzymes, micellar surfactants bearing a mercapto group were synthesized and their catalytic activity in the degradation of p-nitrophenyl carboxylates was studied. N-Hexadecyl-Nα-glutaryl-l-cysteinamide (AM·Cys-1) has an ability to form anionic micelles in aqueous media. The catalytic activity of AM·-Cys-1 was compared with that of another synthetic surfactant, N-hexadecanoyl-l-cysteine (AM·Cys-2). These surfactants below their critical micelle concentrations markedly accelerated the degradation of several p-nitrophenyl carboxylates. On the contrary, the concentration - rate profiles for the degradation of p-nitrophenyl dodecanoate (PNPL) as catalyzed by the surfactants indicate that the reactivity of the mercapto group is reduced upon formation of the anionic micelles. The large rate retardation is primarily due to the decrease in concentration of the active thiolate anion. This was supported by the fact that the pKa values for mercapto groups of the anionic micelles, for which the carboxyl group acts as an anionic head, were increased by 0.8–1.6 pKa unit over those of the corresponding monomeric surfactants in the bulk phase. These surfactants showed profound reactivity even in a neutral pH region when mixed with cationic CTAB micelle. The electrostatic field effect provided by the cationic head of CTAB micelle seems to enhance the nucleophilicity of the mercapto group in the mixed micelles.